The invention relates to novel insect repellents (e.g., 3,8-p-Menthanedilinoleate, also known as PMDL) having ester bonds such that, when deposited on skin, natural cleaving agents in the skin cleave the ester bonds and provide slow release of the repellent active. The invention further relates to a process for slowly delivering (e.g., over time) the insect repellent active to skin or other substrate by providing novel compounds, which are esters of known actives, to the skin or substrate surface thereby allowing skin esterases to cleave ester bonds and release the active.
One of the major technical problems in the area of insect repellent applied to skin is that the skin repellent active (e.g., N,N diethyl diamide, also known as DEET; or para-menthane-3,8, diol, also known as PMD) evaporates too quickly such that the life span of the active is shorter than optimally desirable (e.g., 1 to 2 hours rather than longer, slow release). Thus, it requires constant reapplication.
Methods for controlled release of repellent molecules are known in the art.
EP 348 550 (assigned to Showa Denko), for example, discloses use of microcapsules (filled with diethyltoluamide active) to provide slow release of active. These are referred to as vermin-repellent microcapsules.
EP 502 119 (assigned to Scios Nova) discloses use of solid, water-insoluble lipospheres (formed of a solid hydrophobic core having a layer of a phospholipid embedded on the surface of the core) for extended release of active (e.g., insect control agent).
U.S. Pat. No. 6,015,570 to Tucci et al. discloses a slow release insect repellent, an oleophillic chemical soluble in the insect repellent and a matrix wherein the combination of insect repellent and oleophillic chemical are entrapped in said matrix and slowly released from a substrate (e.g. fabric substrate) containing them.
U.S. Pat. No. 4,774,082 to Flashinski et al. discloses compositions in which polymer is used to decrease volatility of insect repellent and clearly enhance residual activity.
Similarly, U.S. Pat. No. 6,180,127 to Calton et al. disclose use of copolymer of polyvinyl pyrollidone and an alkyl group of 4-30 carbon for slow release of volatile repellent.
In none of these references is there disclosed esters (e.g., saturated or unsaturated, C8 to C30, preferably C12 to C24 fatty acid esters) of specific repellents (e.g., ester of 3,8-p-menthanediol) as novel compounds which can be applied to skin (e.g., solubilized in alcohol solution and applied as alcohol based solution), wherein natural enzymes in the skin (e.g., esterases) are permitted to provide slow release of the repellent active. Use of these esters permits the dual function of delivery of repellent active (cleaved from fatty acid portion) as well as delivery of skin benefit agent (e.g., fatty acid benefit agent such as linoleic acid).
Finally, the underlying actives are not new. Thus, for example 3,8, para-methanediol (known also as xe2x80x9cChinese Crystalxe2x80x9d), used as an example in the subject invention, is a known insect repellent as disclosed in U.S. Pat. No. 5,621,013. Again, however, the use of novel esters of such actives (e.g., 3,8-p-methane linoleate, or PMD-L) as slow release insect repellent is not, to applicants"" knowledge, known.
Suddenly and unexpectedly, applicants have found that esters of insect repellents, e.g., saturated or unsaturated C8 to C30, preferably C12-C24 esters of such repellents serve as slow release compounds, especially when formulated and delivered to skin or other substrates.
In a second embodiment of the invention the invention relates to compositions, which may, but need not, contain surfactant and which compositions may be delivered as leave on or wash off compositions to the skin surface. These compositions, of course, comprise the ester derivatives of insect repellent such as those noted above.
Finally, the invention provides a method for providing insect repellent compound over a period of greater than about 3 hours, as measured by Solid Phase Micro Extraction/gas chromatography of head space above skin or substrate which has been treated with the repellent compound (i.e., repellent active precursor such as, for example, PMD-L).